Basic network troubleshooting

Basic network troubleshooting

Because of the variety of network configurations, operating systems, setup, etc. not all of the below information may apply to your network or operating system.

Note: We cannot assist you with network problems due to an unknown passwords or unknown ISP settings. Since we have no method of verifying or determining this information.

Adapter resources

Device Manager network adaptersVerify that the network adapter is properly installed and detected by the computer with no conflicts. If you're using Microsoft Windows check in Device Manager and verify there are no errors and "Network adapters" is present with each network adapter installed in the computer listed, similar to the example on the right.

    How do I get into Windows Device Manager?

    Identifying problems in Windows Device Manager.

If conflicts exist or the network adapter is being detected as an Other device. The network card has not been properly installed in the computer. Try letting Windows re-detect and install the Network card by removing the network adapter and any other conflict devices from Device Manager and then rebooting the computer. If Windows re-detects the card but does not find the drivers, download the network adapter drivers from the computer manufacturer or the network card manufacturer.

    How do I remove a device in Windows Device Manager?

    Listing of network drivers and network card manufacturers.

Verify connections

Wired Network

Ethernet LAN portIf this is a wired network, verify that the network cable is properly connected and make sure the LEDs next to the network jack are properly illuminated. For example, a network card with a solid green LED or light usually indicates that the card is either connected or receiving a signal. If the green light is flashing, this is an indication of data being sent or received. In the picture is an example of LAN port with two LED indicators next to the RJ-45 port. With this port, one LED will light up if connected properly and the other will flash when transmitting data.

If there are no lights or the lights are orange or red the card may be bad, not connected properly, or that the card is not receiving a signal from the network. If you are on a small or local network and have the capability of checking a hub, switch, or router verify that the cables are properly connected and that it has power. If after checking the connections the LED indicators appear bad, the network adapter, port, or cable may be defective.

Wireless Network

Wi-Fi button on laptopIf you're using a laptop with a wireless network make sure if the laptop has a Wi-Fi button that it is turned on. Many laptops have a Wi-Fi button that allows the wireless network to be turned on and off. In the picture is an example of a Wi-Fi button that is currently enabled.

If the Wi-Fi button is turned on, make sure you're connecting to the correct Wi-Fi hotspot by right-clicking on the Network icon in the Windows notification area and clicking "Connect to a network". Usually, the network with the strongest connection (the most bars) will be your wireless router.

Finally, when connecting to most wireless networks you need to enter the proper SSID (password) in order to connect to the network. If the incorrect SSID has been entered you cannot access the network.

Adapter functionality

Verify that the network card is capable of pinging itself by using the ping command. Windows users can ping the computer from a Windows command line. Unix and Linux users can ping from the shell.

To ping the card or the localhost, type either

ping 127.0.0.1

or

ping localhost

Doing either of the above commands should get replies from the network card. If you receive an error or if the transmission fails the network card is not physically installed into the computer correctly, has the incorrect drivers, or that the card is bad.

Connect to the router

If all of the above steps have been checked and your network has a router, make sure the computer can connect to the router by performing the below commands.

Determine the routers address

Using the ipconfig command (or ifconfig command for Linux) determine the router's address by looking at the Gateway address. Below are the steps for Microsoft Windows users, Linux users can substitute ipconfig for ifconfig.

    Open the Windows command line.

    From the command prompt type ipconfig and press enter. This command should give you an output similar to the example below.

Ethernet adapter Local Area Connection:

Connection-specific DNS Suffix . : computerhope.com.

IP Address. . . . . . . . . . . . : 192.168.1.103

Subnet Mask . . . . . . . . . . . : 255.255.255.0

Default Gateway . . . . . . . . . : 192.168.1.1

The Default Gateway is the address of your router. Most home routers have a gateway address that starts with 192.168 like the address shown above. Assuming your gateway address is 192.168.1.1 attempt to ping the router to see if it can send and receive information by running the below command.

ping 192.168.1.1

If you get replies back from the router, the connection between your router and computer are good, and you can skip to the next step.

If you do not receive any replies back from the router either the router is not setup properly or your connection between the router and the computer are not correct. Reset your router to make sure it is not a problem with your router by following the steps below.

    Turn off the power to the computer and leave it off.

    Unplug the power to your router and cable modem or DSL modem.

    Leave the power cables disconnected for 10-15 seconds and then plug in your modem and then your router again.

    Finally, turn on your computer again and repeat this step to see if you can ping your router.

If you're using a wireless network and have followed all the above steps and still are unable to ping the router try turning off the computer again and connect the computer to the router using a cable instead of trying to connect using wireless. If a wire does also not work connect the manufacturer of the router for additional support or replacement.

Firewall

If your computer network utilizes a firewall, make sure all required ports required are open, especially port 80, which is the HTTP port. If possible, disable the firewall software program or disconnect the computer from the firewall to make sure it is not causing the network problems.

Internet is not working

If you're able to ping the router, but are still unable to connect to the Internet, either your router is improperly configured or the ISP is having issues.

Note: Some ISPs such as Comcast require special software be installed. Make sure any software included with your Modem or other hardware has been installed on at least one computer if you are setting up a new Internet connection.

If your Internet has been working but recently stopped working, give it a few minutes to make sure it is not a temporary outage. If after waiting a few minutes, you still have problems and you have not disconnected the power to your router and modem already follow the steps below.

    Turn off the power to the computer and leave it off.

    Unplug the power to your router and cable modem or DSL modem.

    Leave the power cables disconnected for 10-15 seconds and then plug in your modem and then your router again.

    Finally, turn on your computer again and repeat this step to see if you can ping your router. 

If after following the above steps the Internet is still not working, open the Windows command line and run the below command.

ping google.com

Running the above command should get a reply from Google. If you get a reply, this is an indication that the Internet is working, but you may be encountering a problem with the Internet browser you are using to browse the Internet. Try an alternative browser such as Firefox or Chrome.

If you're getting no reply from Google, your router or modem is not reaching the Internet. If you have a router, make sure your router has DHCP enabled and that the WAN or Gateway address is the proper ISP address.

Finally, after verifying all of the above settings if your Internet is still not working we suggest contacting the ISP to make sure it is not a problem on their end and to assist you further with any special configurations that may not be mentioned in this document.

Additional troubleshooting

Another method of determining network issues is to use the tracert command if you are a Windows user or the traceroute command if you are a Linux or Unix variant user. This command gives you an overview of each of the devices (routers) a packet travels (hops) over a network and can give you an idea of where a problem exists in your network or outside of your network.

To use this command you must be at the command line and type one of the below commands depending on your operating system.

tracert google.com

or

traceroute google.com

If run successfully you should begin to see each hop between the computer and network devices. When the connection fails, determine what device is causing the issue by reviewing the traceroute listing.

Network Troubleshooting: Troubleshooting LANs

Local area networks (LAN) are integral to the operation of many businesses today. The most common LANs use Ethernet, a data link layer protocol, and Internet Protocol (IP), a network layer protocol.

A LAN is comprised of many elements: printers, monitors, PCs, IP phones, servers, storage hardware, networking equipment, security software, network applications, enterprise applications, office productivity applications, and more. Devices on the network are linked physically by twisted pair copper, fiber or wireless access points.

Troubleshooting LAN networks is typically the job for the frontline network support staff - engineers and technicians. Common network troubleshooting problems include user connection issues and slow networks.

Root causes of network troubleshooting problems are frequently caused by one of these three sources:

1. Physical layer: copper, fiber or wireless

Possible causes:

    Damaged or dirty cabling or terminations

    Excessive signal attenuation

    Insufficient cable bandwidth

    Wireless interference

2. Network Layer: Ethernet and IP

Possible causes:

1.     Damaged networking devices
2.     Incorrect or sub-optimal device configurations
3.     Authentication and association issues
4.     Insufficient network bandwidth

3. Switches and VLANs

Possible causes:

•     Excessive utilization
•     Too many errors
•     Incorrectly assigned VLAN membership
•     Traffic priority (CoS/QoS) issues

Best practices for successful LAN troubleshooting include these steps:

1. Identify the exact issue or problem: Have the person who reported the problem explain how normal operation appears, and then demonstrate the perceived problem.

2. Recreate the problem if possible: Ask yourself if you understand the symptoms, and verify the reported problem yourself if possible.

3. Localize and isolate the cause: Attempt to isolate the problem to a single device, connection, or software application.

4. Formulate a plan for solving the problem: Research and/or consider the possible solutions to the problem. Consider the possibility that some solutions to the problem at hand may introduce other problems.

5. Implement the plan: Your actual solution to the problem may be replacing hardware, implementing a software patch, reinstalling the application or component or cleaning a virus infected file. If the problem is the user account, the user’s security settings or logon scripts may need to be adjusted.

6. Test to verify that the problem has been resolved: After you have implemented the solution, ensure that the entire problem has been resolved by having the user test for the problem again.

7. Document the problem and solution: Documentation can be used for future reference to help you troubleshoot the same or similar problem. You can also use the documentation to prepare reports on common network problems for management and/or users, or to train new network users or members of the network support team.

8. Provide feedback to the user: This encourages users to report similar situations in the future, which will improve the performance of your network. If the user could have done something to correct or avoid the issue, providing feedback may reduce the number of future network problems.

Importance of LAN troubleshooting tools and training

Giving frontline network support staff the proper training, the right tools, and a solid network troubleshooting methodology results in faster LAN problem solving - saving staff time, closing trouble tickets quicker, minimizing downtime, and getting network users back to productivity faster.

Network troubleshooting tools are a necessity for every network administrator. When getting started in the networking field, it is important to amass a number of tools that can be used to troubleshoot a variety of different network conditions.

While it is true that the the use of specific tools can be subjective and at the discretion of the engineer, the selection of tools in this article has been made based on their generality and common use. This article reviews the top 10 basic tools that can help you troubleshoot most networking issues.

10. Ping

The most commonly used network tool is the ping utility. This utility is used to provide a basic connectivity test between the requesting host and a destination host. This is done by using the Internet Control Message Protocol (ICMP) which has the ability to send an echo packet to a destination host and a mechanism to listen for a response from this host. Simply stated, if the requesting host receives a response from the destination host, this host is reachable. This utility is commonly used to provide a basic picture of where a specific networking problem may exist. For example, if an Internet connection is down at an office, the ping utility can be used to figure out whether the problem exists within the office or within the network of the Internet provider. Figure 1 below shows an example of the ping utility being used to obtain the reachability status of the locally connected router.

ping: Ping utility

9. Tracert/traceroute

Typically, once the ping utility has been used to determine basic connectivity, the tracert/traceroute utility can used to determine more specific information about the path to the destination host including the route the packet takes and the response time of these intermediate hosts. Figure 2 below shows an example of the tracert utility being used to find the path from a host inside an office to www.google.com. The tracert utility and traceroute utilities perform the same function but operate on different operating systems, Tracert for Windows machines and traceroute for Linux/*nix based machines.

 Tracert/traceroute utility

8. Ipconfig/ifconfig

One of the most important things that must be completed when troubleshooting a networking issue is to find out the specific IP configuration of the variously affected hosts. Sometimes this information is already known when addressing is configured statically, but when a dynamic addressing method is used, the IP address of each host can potentially change often. The utilities that can be used to find out this IP configuration information include the ipconfig utility on Windows machines and the ifconfig utility on Linux/*nix based machines. Figure 3 below shows an example of the ifconfig utility showing the IP configuration information of a queries host.

Ipconfig/ifconfig

7. Nslookup

Some of the most common networking issues revolve around issues with Dynamic Name System (DNS) address resolution issues. DNS is used by everyone using the Internet to resolve commonly known domain names (i.e. google.com) to commonly unknown IP addresses (i.e. 74.125.115.147). When this system does not work, most of the functionality that people are used to goes away, as there is no way to resolve this information. The nslookup utility can be used to lookup the specific IP address(es) associated with a domain name. If this utility is unable to resolve this information, there is a DNS issue. Along with simple lookup, the nslookup utility is able to query specific DNS servers to determine an issue with the default DNS servers configured on a host. Figure 4 below shows an example of how the nslookup utility can be used to query the associated IP address information.

 Nslookup utility

6. Netstat

Often, one of the things that are required to be figured out is the current state of the active network connections on a host. This is very important information to find for a variety of reasons. For example, when verifying the status of a listening port on a host or to check and see what remote hosts are connected to a local host on a specific port. It is also possible to use the netstat utility to determine which services on a host that is associated with specific active ports. Figure 5 below shows an example of the netstat utility being used to display the currently active ports on a Linux machine.

Netstat Netstat utility

5. PuTTY/Tera Term

When connecting to a variety of different types of equipment, a telnet, SSH or serial client is required; when this is required both the puTTY and Tera Term programs are able to provide these functionalities. The selection of one over the other is strictly a personal preference. Figures 6 and 7 below show both puTTY and Tera Term being used to connect to a host via SSH.

PuTTY

Tera Term

4. Subnet and IP Calculator

One of the most important tools in the belt of a junior network engineer is an IP network calculator. These can be used to unsure a correct IP address selection and with this a correct IP address configuration. While this type of tool is used by senior level network engineers, much of the information obtained from the tool becomes simpler to calculate the longer and more experience you have in the field. Two of the more commonly used free IP calculators include Wildpackets (Bitcricket) Network Calculator and Solarwinds Advanced Subnet Calculator which can be found at the links below.

http://www.bitcricket.com/downloads/IPCalculator.msi

http://downloads.solarwinds.com/solarwinds/Release/FreeTool/SolarWinds-Subnet-Calculator.zip

Subnet and IP Calculator

Figure 8: Subnet calculator

3. Speedtest.net/pingtest.net

A very easy test that can be used to both determine the Internet bandwidth available to a specific host and to determine the quality of an Internet connection is the use of the tools available at the speedtest.net and pingtest.net websites. The speedtest.net site provides the ability to determine the amount of bandwidth that is available to a specific host at a specific point in time; this is often a good tool to use when measuring how long it is going to take to upload or download information from a local to remote host. This measurement can also be used to determine whether the connection is offering the amount of bandwidth that was purchased from the Internet provider; keep in mind however that some amount of bandwidth difference is expected between the quoted bandwidth purchased and the measured bandwidth. The pingtest.net website is used to determine the quality of the connection by measuring the ping response times and jitter amounts over a short period of time. This information can be used to determine a likelihood of how well the measured connection will deal with certain types of high demand traffic like Voice over IP (VoIP) or gaming. Figure 9 and 10 below show example output from both of these sites.

 Speedtest

 Pingtest

2. Pathping/mtr

In an effort to take advantage of the benefits of both the ping and tracert/traceroute commands, the pathping and mtr utilities were developed. Both of these tools take the functionality and information that can be obtained from these types of tools and provide a more detailed single picture of the path characteristics from a specific host to a specific destination. Figure 11 and 12 below show examples of these two tools and what information they provide.

Pathping

 Mtr

1. Route

The last of the tools covered in this article is the route utility. This utility is used to display the current status of the routing table on a host. While the use of the route utility is limited in common situations where the host only has a single IP address with a single gateway, it is vital in other situations where multiple IP address and multiple gateways are available. Figure 13 below shows an example of the route utility being used on a Windows machine.

Route: Route Utility

As with any job, the type of tools that are quickly available can greatly influence the amount of time that it takes to complete a job. When troubleshooting a networking issue, the amount of time that it takes to find and fix a problem directly affect the wasted costs that it causes to any system relying on the network. This article has taken a look at the 10 most commonly used tools that can help in ensuring that the time that it takes to find and fix a problem is as short as possible. I hope the information in this article can be helpful in future troubleshooting.